718 
MR. W. BEVAN LEWIS ON THE COMPARATIVE 
characterised by a rich confluent and deep belt of cells coextensive with a four- 
laminated cortex. Such a formation extends over the anterior half of the upper limbic 
arc, and stretches upwards and outwards over the exposed aspect of the hemisphere. 
By iar the richest formation lies in the latter position—viz. : on the exposed aspect of 
the vault, in a lengthened strip of territory lying parallel with the great longitudinal 
fissure, and represented by the shaded area in the diagram. -3 ' It extends forwards 
well into the frontal extremity, covers the whole outer aspect of the hemisphere here, 
and becoming much poorer in cells, spreads along the lower confines of the extra-limbic 
mass, skirting the limbic fissure as far as, and even behind, the slight depression which 
in this animal represents the Sylvian fissure. Between these two tracts the enclosed 
area is spanned by a jive-laminated cortex whose ganglionic series is poor, and 
distributed in the linear or solitary arrangement. The region which may therefore be 
considered, par excellence, as that of a rich ganglionic formation, is the narrow strip 
of cortex along the sagittal margin of the hemisphere from A to D (Plate 4.9, fig. 3), 
extending over the outer aspect of the hemisphere betwixt A and B as far down as the 
limbic fissure, and next to this the upper limbic arc. The far less characteristic 
formation adjacent to the limbic fissure, however, is interesting chiefly from the fact 
that it foreshadows a richer structure, which appears along this course in higher 
animals. It will be convenient to name these formations the sagittal and Sylvian 
formations of large ganglionic cells. Thus it was shown that the five-laminated cortex, 
with its clustered cells, in the Pig not only extends over the anterior limbic arc and 
frontal lobe, but bends back over the first and second parietal gyri “ from their union 
with the ascending parietal (post-Bolandique, Broca) towards and around the Sylvian 
fissure. ;, t In the Pig, therefore, as also in the Sheep, we have demonstrated the 
distribution of the rich ganglionic layer over the regions bordering upon the limbic 
fissure. Just as in these and other allied animals we have betwixt the two regions of 
the clustered ganglionic cells an intermediate district characterised by a laminar 
arrangement of this series and an intercalated series of angular elements, so in the 
Babbit a similar cortex intervenes betwixt the inner and outer series of rich ganglionic 
areas. We thus conclude that the fundamental type of the structure of the cortex 
over the extra-limbic and upper limbic realms is identical in these various animals. The 
dense layer of ganglionic cells bordering upon the great longitudinal fissure maintain a 
fair uniformity of size throughout. A large number of measurements give the 
following average dimensions :— 
* Area shaded by small crosses, Plate 49, fig. 1. 
t See fig. 3, p. 44, “ On the Comparative Structure of the Cortex Cerebri.” Phil. Trans., Part. I., 1880. 
